Magazine

Apr - Jun 1994

Between July 16 and 22 this year, the planet Jupiter will be struck by the fragments of comet Shoe­maker-Levy 9, 1993e.
Moving at very high speed, these projectiles—perhaps up to 4 km in diameter—are expected to explode deep within Jupiter's outer layers, providing us with a unique opportunity to learn more about this enigmatic planet.
Unlike Venus, which has a solid surface lurking beneath its dense clouds, Jupiter is a giant ball of gas and fluid. The upper layers are clouds composed of droplets or crystals of ammonia and water. Beneath the clouds is a transition zone of slush overlying a liquid core of hydrogen and helium, with only a small amount of rock in the very centre.
Over the last 50 years a great deal of observational work has been done on Jupiter: spectrographic analysis, radio emissions, infra-red radiation record­ings by spacecraft, and recording of the weather patterns in the upper atmosphere. Large spots, swirls and bands apparent in photographs are thought to represent storms and jet streams, but although their intensity changes, they appear remarkably stable. The Voyager 1 and 2 spacecraft provided much of this information in March 1979.
But for all this, our understanding of the planet is very far from complete, which is why the Galileo probe was launched in 1989. As well as orbiting Jupiter, Galileo has an instrumented capsule to release (probably within the next two years), which will para­chute down, transmitting data until it is crushed by the increasing atmospheric pressure.
All the solar system bodies which show signs of extensive cratering exhibit the occasional curious chain of craters—a phenomenon most plaus­ibly explained by a swift succession of strikes by bodies such as a recently fragmented cometary nucleus. Such combina­tions of fragmentation and collision with a planet probably only occur, on average, once in tens of thousands of years; per­haps just once since our species started making any sort of astronomical observations. Although on the scale of the universe's putative age—five billion years—a once-in-20,000­ years event is common­place, compared with the 50-year working life of the average clean-living astronomer, it is unique!
Thus the prediction of a collision of a fragmented comet, Shoemaker-Levy 9, with Jupiter in mid-July has aroused intense interest amongst astrono­mers all over the world.
Discovered photographi­cally in March last year, Shoemaker-Levy, in orbit about Jupiter rather than the Sun, already presented an unusual appearance, and was described as "squashed." In fact, by this time the comet had already been pulled apart by the Jovian gravitational field as it swung close above the planet's cloud tops on its 1993 approach. (Unlike planets and moons, which are large enough to de­velop their own gravita­tional fields which then hold them together, comets are aggregations of low density material that easily disintegrate.)
Earlier photographs of the area inhabited by the comet show no sign of it, as the nucleus was still intact and too faint for detection. Photographs this year, particularly those taken with the recently repaired Hubble Space Telescope (one of NASA's greatest technical feats), show 21 fragments lined up like beads on a neck­lace, with the brightest in the middle and the faintest at the ends. Keeping perfect formation, these fragments of the original nucleus are now hurtling towards Jupiter and their terminal encounter.
More recent photo­graphs show that most of the "dust" which normally accompanies a comet fragmentation has disap­peared. This is quite unexpected, and some astronomers now think that S-L9 may have originated as an asteroid rather than a comet. In any case, the fragments, the larger ones being at least a kilometre in diameter, and perhaps as much as four kilometres, will enter the upper reaches of the Jovian atmosphere at 60 km/s (216,000 km/h, equivalent to a 1 h 40 m flight to the Moon from Earth).
On average, each fragment will be arrested after penetrating up to 150 km below the top of the cloud layer and will release energy equivalent to hundreds of thousands of megatons of TNT. This will result in a fireball such as is seen in a nuclear explosion (although the largest atmospheric nuclear explosion was a mere 58 megatons, deto­nated by the Soviet Union in 1961) which will rise far above the cloud tops and spread out in the strato­sphere for 2000-3000 km. This fireball will be, for just over half a minute, as bright as the whole planet, and its light will shine on the inner moons, Io and Europa.
Because the comet has, at the time of writing, been observed for less than half of its orbit, and there are inherent uncertainties which limit the accuracy with which the position of such a body can be pre­dicted, the times of impact (see table) are only good to within ±45 minutes, although the collision site on Jupiter is already fairly certain. Impact times of the fragments will be deter­mined to within a few minutes closer to the events.
Sweeping in from the south—above, as we see Jupiter in our sky—the train of fragments will arrive in succession over a period of five-and-a-half days. all striking between Jovocentric latitudes 44°S and 45°S. All impacts will occur on the night side of the planet, and because of the Earth's small angular distance from the Sun as seen from Jupiter, this means that the collisions will be just over the night-side horizon (see diagram).
Although we will not have a direct view, never­theless we may be able to observe the impacts indirectly. First, there is the short-lived flash which may be seen as a brighten­ing of either of the moons Io or Europa, which, together with their outer companions Ganymede and Callisto, are easily seen with binoculars. Alternatively, as the planet rotates (a complete Jupiter rotation takes just less than 10 hours) it may bring into view signs of the distur­bance caused by the collision. To see these effects, the observer will need to be familiar with the appearance of the planet beforehand, for the changes in appearance will probably be subtle.
The spacecraft Galileo will be 240 million kms from Jupiter (roughly one third of Earth's mean distance from the planet) at the time of impact, and will have a direct view of events. Unfortunately, its camera can capture only one photograph every two­-and-a-half seconds, and relaying the images back to earth will take many weeks, on account of equipment failures that have shrivelled its operational capacities.
Each of the impacts will he, in effect, an astrophysical experiment. Because of remoteness, extreme temperatures and/ or size of the objects of their study, astronomers cannot perform experi­ments in the classical sense. Not for them the isolated sample subjected to carefully controlled changes in physical or chemical conditions.The astronomer is condemned to wait upon the course of events and to make the best of the observational data available.
The Shoemaker-Levy 9 fragments constitute a very dirty probe, and the event will be about as elegant as an experiment by William Brown of Just William notoriety. But this is all there is on offer, and during July there will be a worldwide effort by astronomers using every type of detector to monitor the events.
The sheer energy of the collisions (some claim hundreds of times that which was released in the collision that is thought to have been responsible for eliminating the dinosaurs 60 million years ago), the extent of their shock waves, and the depth within the Jovian atmos­phere from which they may eject material is far in excess of anything we could hope to engineer.
Just what will be seen and discovered as a result of these events is highly conjectural. In general terms, however, we can reasonably expect to discover a good deal about the chemistry of the lower levels of the Jovian atmos­phere, and hope that significant light will be shed on the physics of this extraordinary atmosphere, with its coloured cyclonic storm the Great Red Spot (first seen in 1664) and complex circumplanetary cloud bands.
It is paradoxical that Venus, with its mountain­ous surface, presents us with a surprisingly bland sheet of cloud wrapping the planet from pole to pole, whereas Jupiter, innocent of such impedi­ments to the smooth flow of its atmosphere, shows a spectacular complex of globe-engirdling jet streams and chains of nonstop hurricanes in its violent atmosphere.

Rain fell from overcast skies and gale force winds drove large waves on to the beaches of Normandy as dawn broke on Monday June 5,1944. To the Germans watching from their defences, there was nothing to show that this was the moment the Allied Armies had planned to invade Europe. In fact, the operation had been put on hold because the bad weather had been forecast 24 hours before. Had it gone ahead in these conditions, the invasion would have been a cata­strophic failure.
Nevertheless, the invasion had to occur on either the 5th, 6th or 7th of June to take advantage of the right conditions of moon and tide. Darkness was needed when the airborne troops went in, but moonlight once they were on the ground. Spring low tide was necessary to ensure extreme low sea level so that the landing craft could spot and avoid the thousands of mined obstacles that had been deployed on the beaches. If this narrow time slot was missed, the invasion would have to be delayed for two weeks.
The decision to post­pone the invasion for 24 hours had been taken by Eisenhower and the Supreme Command at 0430 on Sunday June 4. It was not taken lightly, because so many ships were already at sea con­verging on Normandy that the risk of detection was grave.
Nor had the forecast which prompted the postponement been easily arrived at. Eisenhower's weather advice was provided by Group Captain Stagg, a forecaster sec­onded from the British Meteorological Office who was coordinating the advice of three forecasting teams: one from the Meteorological Office, one from the Admiralty and one from the United States Army Air Forces.
The advice of these groups was often diametri­cally opposed. The Ameri­can team used an analog method, comparing the current map with maps from the past, and were often over-optimistic. The Meteorological Office, aided by the brilliant Norwegian theoretician Sverre Petterssen, had a more dynamic approach, using wind and tempera­ture observations from high altitude provided by the air force, and were closer to the mark.
The decision to invade on Tuesday June 6, taken late on Sunday night and finally confirmed early Monday morning, was based on a forecast of a short period of improved weather caused by a strengthening ridge following the front that brought Monday's rain and strong winds. In the event, Monday's bad weather had already given the Allies a crucial advantage: it had put the Germans off guard.
The Germans were uncertain when and where the invasion would come, but had been led to believe the most likely place was Calais and the most likely time was July. Hitler, however, had long under­stood that the key to anticipating the timing of the invasion would be good weather forecasting.
But by the summer of 1944, German weather forecasters in France were hampered by a lack of weather observations over the Atlantic, because their submarine fleet was now much depleted and the Luftwaffe had largely yielded the skies to the RAF. Consequently, their forecasters could not detect the subtle changes that would lead to a temporary improvement starting on Monday evening.
Rommel, the general commanding the defence of the invasion beaches, had identified the period June 5, 6 and 7 as high risk because of the state of the moon and tide. However, he also believed the Allies would not attempt an invasion without a guaran­tee of six days' fine weather. Reassured by the Luftwaffe weather forecast­er's prediction that the bad weather starting on Monday the 5th would last at least three days, Rommel left France for Berlin. There he hoped to persuade Hitler to relin­quish his personal control of the Panzer reserves in Holland and France to either himself or Von Rundstedt, who had overall command in the west. (As it transpired, Hitler held most of the reserves in the north, near Calais, for almost two months after the Normandy invasion, because he was persuaded Nor­mandy was only a diver­sion.)
Consequently, Rommel was in Germany when the invasion began, and only made it back to the front at the end of the first day.
The German Navy also dropped their guard when the bad weather com­menced, and did not patrol the channel. Only five weeks before, some of their torpedo boats had crossed the Channel and attacked a night-time dress rehearsal for the landings. In ten minutes, they sank two landing craft, crippled a third and killed over 600 sailors and soldiers.
But on the Monday night when the invasion fleet of over 6000 ships crossed the Channel, the torpedo boats did not venture out until 4 AM-after the fleet had been detected from the French shore. By this time the fleet had been anchored about 15 km off the beaches along a front of 100 km for more than an hour.
The weather on June 6 was tolerable but not ideal. Strong winds scattered the paratroops, some of whom overshot the Cherbourg Peninsula and landed in the sea and were drowned. However, the Germans were also obliged to scatter their defences.
Large waves swamped 27 out of 32 amphibious tanks, and all the artillery was lost on the run in to Omaha beach, where the Allies suffered their greatest losses of the day and briefly considered withdrawing. At the end of the first day, Allied casualties were 12,000 killed, wounded and missing, as against an estimated 75,000 if sur­prise had not been achieved.
The weather that northern summer was among the worst on record. Several days after the landings, a storm wrecked one of the artificial harbours that had been built and caused four times the losses in ships and equipment that occurred during the landing.
Two weeks later, in the second time slot suitable for the invasion, another major storm occurred, prompting Eisenhower to send Stagg a letter saying, "I thank the Gods of war we went when we did."
Some of the most famous seaborne inva­sions in history have come to grief because of the weather. Although The Spanish Armada was defeated by Drake's English fleet, it was the storms that followed the battle that decimated it.
In 1281, Kublai Khan, the Mongol Emperor of China, attempted to invade Japan with an army of 150,000. The Mongols fought the Japanese for weeks, trying to establish a beachhead, until the invasion fleet was destroyed by a storm, subsequently named Kamikaze or divine wind by the Japanese.
In New Zealand, the weather has also played a crucial role in warfare. In the Land War in south Taranaki in 1868, the Ngaruahine leader Titokowaru had some 80 warriors at his disposal, compared to nearly 1000 in the colonial forces under McDonnell.
In order to provoke McDonnell into pursuing him into the bush and fighting him on ground of his own choosing, Titokowaru attacked a redoubt at Turuturu Mokai near Hawera, only three miles from the main camp of the colonial army. Titokowaru chose to attack just before dawn on a day when a strong westerly wind was blowing so that the sound of gunfire would not reach the main camp—a mere twenty minutes' cavalry ride away. The attack was successful, with 16 colonial casualties as against 6 for Ngaruahine.
Two months later, McDonnell attacked Titokowaru's stronghold in
the bush and suffered one of the greatest defeats in New Zealand history, with many killed, including Major Von Tempsky.
The weather also played a decisive role when Te Rauparaha besieged Ngai Tahu in their pa at Kaiapohia (old Kaiapoi) in 1831. Built on a peninsula in a swamp, the pa could be attacked from only one side, which was protected by a strong palisade. Deep zigzag trenches were dug up to the palisade, and, under cover of darkness, manuka was stacked high against it so the attacking force could burn its way in. But before setting fire to the manuka, they needed a southerly wind to blow the flames against the palisade
Instead, a northwest wind developed. The Ngai Tahu defenders knew that a northwest wind in this area was almost always followed by a southerly, so they set fire to the manuka in order to burn it out before the southerly came. But the wind changed quickly, the palisade burned, and the pa was taken with considerable loss of life.
Correctly forecasting the weather for D-Day was crucial to the success of the invasion, which, if it had failed, could not have been repeated for another year. For the rest of his life, in moments of stress, Group Captain Stagg would remember some words spoken to him in the tension-filled days leading up to the post­ponement by General Morgan, Eisenhower's Chief of Staff: "Good luck, Stagg; may all your depressions be nice little ones: but remember, we'll string you up from the nearest lamp post if you don't read the omens aright."

It was, of course, a great event in the social history of the Far South of the West Coast, where wed­dings are by no means everyday happenings. The wedding was to take place about halfway down between the last of the bridges and the end of habitation. So, as the great day approached, one cavalcade of riders, men and women, travelled up the pack-tracks and beaches from the south, while a similar group rode down from "the end of the wheel-track road" in the north.
I was with the northern contingent. We were about twenty strong, and a very cheerful party too, strung out along the pack-track, or gathered into more socia­ble groups where riverbed or beaches gave us room to bunch together for a bit. Every now and then the musicians among us would burst into song (to the great consternation of the birds in the bush) and the rest of us would join in the choruses, at the top of our voices, every man in his own key. The miles, which can seem mighty long when you travel alone, slipped by very pleasantly.
We had timed our journey carefully so as to arrive at the scene of the wedding the evening before the ceremony. But then, as so often happened in the days before the bridges, the West Coast weather took a hand. "The sea went round to the north," as the curious expression of the Coasters has it. It makes sense because as you travel along that narrow strip of land between the great ranges of the Southern Alps and the wild steep beaches of the turbulent Tasman, the sound of the breakers is always in your ears. Naturally you hear the distant roar most clearly down the wind, so that when the wind changes from, say, south-west to north-west, instead of hearing the breakers to the south, you hear them roaring in the north. So "the sea has gone round to the north," and it is the nor'-wester driving in, warm and moist from the sea, and coming into collision with the snowy Alps that gives Westland its phenomenal rainfall So, when the North starts roaring, the traveller does some quick thinking about any rivers that may flow between him and his destination, and takes appropriate action.
The whole cavalcade seemed to be saying at once: "The sea's gone round to the north"—and the rain would be pouring down any time now, in buckets....
We had lots of wild little creeks ahead of us, and three rivers, two of them not very difficult, but the last and largest notori­ous for the speed with which it rose and its danger when in flood. So the cavalcade began to crack on the pace. And then the storm hit us. Great rolling black clouds raced in from the sea and the rain came down in a grey wall of water that limited visibility to about fifty yards. It was coming down in streaks about as thick as your thumb. When we pounded across a shingle creekbed, the fall of the water was raising a spray about a foot high where the great drops splashed on the stones. I remember being annoyed (and not for the first time) because the splash of the rain on the shoulders of my oilskin was wetting my ears under the overhang of my sou'wester.
"Do you think we can beat the flood to the ford of the big river?" shouted somebody.
"I very much doubt it," answered one of the old hands, "but we'll give it a go."
So on we moved at a spanking trot, as that's the best pace to cover the miles and the rough going quickly. I was deeply interested by the quiet but effective way two or three of the old hands organised our cavalcade. An experi­enced man was put in the lead, to negotiate any stream and river crossings. Then followed the slowest travellers, so that no one would be left behind—not that anyone was particu­larly slow. Everyone rides good horses on a journey. The rest of the old hands were distributed along the line, to give help or encouragement if needed: and a thoroughly compe­tent man brought up the rear. It seemed as if it was all arranged without anybody saying anything, though I caught an odd word or nod from one old hand to another.
There was no talking or singing now—for one thing it couldn't have been heard—as we belted along through the bush, the pack-track sometimes rough and rocky, some­times muddy, with long pools of surface water. The interval between riders was just enough to make sure that the horse in front didn't throw mud in your eye. The sky was deeply overcast and, in the heavy bush, the track was in twilight.
The creeks were foam­ing a bit but they gave us no trouble. Each rider, as he crossed, waited until the one behind him was safely over, and then went ahead at a walking pace until all were across, and then the shouted word came along the line: "Let her go," and we all broke into a trot again, deter­mined to make that wedding, come heaven or high water.
The first of the smaller rivers was just beginning to rise when we came to it, and the cavalcade waded straight through, on a ford picked by the leader. No trouble. But some of the women of the party were beginning to get a bit weary, good riders though they were, and we'd slow up to a walking pace now and then, and it was pretty welcome, too. The next river was up a bit, swirling along and very discol­oured. So its crossing was treated with a little more care—the dinkum pioneer treatment our grandparents used when travelling a wild, untamed New Zealand.
We formed up in groups of threes, the tallest horse in each group on the upstream side, to break the force of the current; the next horse, on the downstream side and slightly behind, with his head opposite the leader's shoulder: and the third horse again slightly behind, his head opposite the shoulder of the horse in the middle. So we crossed steadily, everyone carefully keeping station. The water came rushing strongly, hungrily, and reached up licking round the saddle­flaps—quite deep enough to give everyone a good bootful and, of course, straight off the mountain ice.
It was three or four miles on to the only two little bush houses on our side of the Big River, and we urged our tired horses to their best pace to cover the distance. One of the residents was standing in his doorway to greet us.
"Any chance of getting across?" I called to him.
"Not a hope in the world. She's as wild as a hawk—running a banker and rising about a foot a minute. You couldn't possibly put a boat on it if you had one."
But I wasn't going to be stopped on hearsay, so I rode on the halfmile or so to the river itself, and a couple of the other men came with me. The river was tearing along, a quarter of a mile wide, carrying logs and stumps and great forest trees that thrashed about as their roots, often weighted with clay and rocks, struck some obstruction on the riverbed. No. Not a hope in the world of getting across there.
But I was a bit jealous of a reputation I had for not being easily stopped—and especially on an occasion like a wedding. So I turned and rode up the bank of the river for a mile or so, looking for any place where there'd be a chance of getting across. I didn't find one, but I came to a place where the flood ran deep and silent through a perpendicular-sided cutting it had made in a gravel terrace. It was only about 150 yards from the top of one fifty-foot bank to the other. I had a good look at it, and made up my mind that, if I couldn't get my body across, I could at least get my voice across. And with that I turned and rode thoughtfully back to rejoin the rest of the party.
The rain was easing off, and the first remark I heard was: "The sea's gone round to the south and it will be fine tomorrow."
"How long will it be before the river goes down?" I asked one of the residents.
"A week at least," he said, "with all that mild rain on the snow."
There was just one telephone line that ran away down to the end of habitation—a good stout 8-gauge fencing-wire, often stapled from tree-trunk to tree-trunk beside the packtrack. All the little settlements were connect­ed to it. So that evening I got into touch with a much-troubled bridegroom in the next settlement across the river. We discussed the situation. He had all the necessary papers ready on his side of the river—and what was the use of that? To his astonished delight, I told him that if he and his bride and their witnesses would come up to "the narrows" at the time fixed—ten the next morning—I and the party from the north would come up on our side, and, if I could hear their responses, I'd marry them across the river.
There was much mirth in our northern camp when I told them what I proposed to do. As some­times happens on the Coast, after "the sea has gone round to the south," the next morning was crisp and cloudless and calm. Punctual to the minute, my northern party ranged themselves round me. I'd put on my cassock and surplice and advanced to within a few feet of the cliff's edge. The bride and groom and their party ranged themselves on their side of the river according to the instructions I'd given over the phone the night before. I was de­lighted to find how easily my voice carried across in the clear still morning air. It was a beautiful setting for a very reverent, if some­what unusual service.
All went well until it came to the place where I asked the groom: "Wilt thou have this woman to thy wedded wife?"—and so on—at which he was overcome with shyness, and just mumbled.
"Can't hear what you say," I called.
The bride gave him a dig in the ribs with her elbow and said, very audibly, "Speak up." And he did!
When it came to her turn I asked her: "Wilt thou have this man to thy wedded husband?" and she cupped her hands before her mouth and shouted "I will," with the utmost audibility. The northern contingent, I regret to say, let out a gust of laughter, and cheered lustily. But they were soon quiet again, and so that the nice buxom bride shouldn't feel put out of face: "Good girl," I called, "I heard that all right," and went on with the service.
So I gave them my blessing across the river.
That was a good many years ago: but, as far as I know, they've lived happily ever after.
All the liquid refreshments for the wedding breakfast hap­pened to be on our side of the flood, their transfer having been blocked by the sudden rise of the river on the previous day. All the glasses were with the south­erners. But we raised our bottles in enthusiastic salute to the bride and groom—a gesture which was greeted with howls and yells of rage and frustration.
Courteously, we offered to try and float a bottle or two across to them.
But, of course, the only bottle that will float is an empty one...

For five days each summer, 1000 fisherman fling themselves into the surf of New Zealand's longest beach in the hope of landing the grandaddy snapper that will win them $50,000. This year's contest was the most successful ever.

For four decades, John Johns has roamed the forests of New Zealand, making pictures that have opened people's eyes to this country's woodland heritage. As official photo­grapher for the New Zealand Forest Service, his brief was to promote the principles of sustainable forestry. As a conservationist and artist, he enables us to see something more than logs and board feet. Through his images, we renew our vision of the forest.

Found only in that narrow strip of Earth where ocean meets land, seaweeds soften the angles of the rocks and build forests and gardens beneath the wave. Richly diverse in colour and form, they are the fundamental food source of marine animals, and contribute more than we generally realise to everyday human life. Tide pool at Army Bay, 25 km north of Auckland, provides both a playground and a window of fascination into the sea.